Boranes as photographic stabilizers

ABSTRACT

SILVER HALIDE PHOTOGRAPHIC EMULSIONS CONTAINING BORANES AS STABILIZERS AND ANTIFOGGANTS.

United States Patent 3,725,078 BORANES AS PHOTOGRAPHIC STABILIZERS John Howard Bigelow, Rochester, N.Y., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del. No Drawing. Filed Aug. 30, 1971, Ser. No. 176,308 Int. Cl. Gtl3c 1/34 U.S. Cl. 96-409 14 Claims ABSTRACT OF THE DECLOSURE Silver halide photographic emulsions containing boranes as stabilizers and antifoggants.

BACKGROUND OF THE INVENTION Field of the invention.This invention relates to photographic silver halide emulsions containing improved foginhibiting compounds and to photographic elements comprising layers of said emulsions. More particularly, the invention relates to photographic'silver halide emulsions containing borane compounds described herein as stabilizers against the formation of fog.

Description of the prior art-The sensitivity of silver halide emulsions may be increased by the addition of labile sulfur compounds, a noble metal, a polyoxyalkylene derivative, a reduction sensitizer such as formaldehyde, etc. On the other hand, the addition of such compounds imparts a tendency for the emulsion to fog as indicated by the reduction of silver salts during development where no exposure has occurred. This tendency is especially harmful during storage under tropical conditions.

In order to inhibit this tendency to fog there have been proposed a great number of compounds as being effective in preventing fog when added to the silver halide emulsions or in layers contiguous with coated layers of the emulsions. In the vast majority of cases, however, the compounds proposed and employed for this purpose have either provided only marginal improvement or have shown certain disadvantages such as loss of speed, or otherwise deleteriously affected the sensitometric characteristics of the emulsions to which they have been added. The loss of speed is particularly pronounced in those emulsions to which have been added non-optical sensitizers, e.g., gold, labile sulfur compounds, etc.

SUMMARY OF THE INVENTION According to this invention, it has been found that silver halide emulsions, to which borane compounds of the general formula given below have been added after the silver halide is precipitated and washed, are resistant to the formation of fog and stabilized during aging without causing a reduction in speed. The general formula of the compounds is as follows:

M is any cation, e.g., H NHJ, Cs+, [(CH ).,N]+,

alkali metal cations, etc.;

X is an electrophilic moiety having a total valance of b;

a is an integer from 1 to 2;

b is an integer from 1 to 12; and

c is an integer from 1 to 2.

These compounds are borane acids and salts having anions with a skeletal framework forming a polyhedron having 12 boron atoms in the framework and in which there are from 1 to 12 electrophilic substituents attached to the boron atoms in the compound. Electrophilic substituents include the groups: halogen, amino, azide, carboxyl, carbonyl, etc. The compounds are usually added at any stage after the emulsion has been formed and washed 3,725,078 Patented Apr. 3, 1973 to remove excess salts formed during the precipitation stage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The borane compounds described herein can be used to stabilize and inhibit fog in a wide variety of negativeworking, developing-out photographic silver halide emulsions including X-ray emulsions, seismographic emulsions, variable contrast emulsions and panchromatic negative emulsions to name a few. The concentration of the borane compounds may be varied over a wide range but good results are usually achieved when they are used in concentrations of from 1O to 10- moles per mole of silver halide. These borane compounds have the general formula set forth above, wherein the moiety represented by X is the electrophilic substituent, or group of substituents, on the boron atoms of the polyhedral anion. The total valence of the X substituent(s) is equal to the number of hydrogens replaced thereby on the anion, i.c., b. A Wide variety of substitutents may be employed; generally, any element or radical capable of bonding to the carbon of a benzene nucleus by replacement of a hydrogen bonded to said carbon is useful.

Typical and representative compounds within the scope of the general formula set forth above include Methods of preparation of the compounds may be found in, The Chemisty of Boron and its Compounds, E. L. Meutterties, John Wiley & Sons, New York, 1967, Polyhedral Boranes, E. L. Meutterties and W. H. Knoth, Marcel Dekker, Inc., New York, 1968, and in Miller and Meutterties, US. Pat. 3,551,120, patented Dec. 29, 1970.

The borane compounds are added after the silver halide is precipitated and washed in conventional processes of preparing negative-working, developing-out silver halide emulsions. In such processes, the silver halide emulsion is formed in an aqueous medium and is then precipitated. It may then be ripened, Washed and remelted as exemplified herein. Preferably, the borane compounds are added during the stages of remelting after washing to remove excess salts remaining after precipitation, before, during or at the end of the digestion period, or as an addendum just prior to coating. The borane compounds may be added to the emulsions as a solution with a suitable solvent, e.g., Water. Generally, water or solvents which are miscible with water are preferred, e.g., ethyl alcohol, acetone, dioxane, etc. The process of preparing the novel emulsions, as described above and exemplified herein, is also within the scope of the invention.

The novel stabilizers or antifoggants of this invention may be used alone or with other fog-inhibiting agents in the silver halide emulsions, e.g., 4hydroxy-6-methyl1,3, 3a,7 tetrazaindene, benzotriazole, 1 phenyl 4 mercaptotetrazole, etc.

The use of the boran compounds of this invention in silver halide emulsion does not interfere with the functions of various additives including optical and nonoptical or chemical sensitizers, e.g., gold salts, labile sulfur, polyalkylene oxides, etc.

Silver halide emulsions which can be stabilized according to this invention can also contain conventlonal additions such as plasticizers for the colloid carrier for the silver halide crystals, coating aids, hardeners such as aldehyde hardeners, e.g., formaldehyde, mucochloric acid, glutaraldehyde, etc. Optical sensitizing dyes, e.g., cyanmes, carbocyanines, merocyanines, etc. may be added to the emulsion system.

The novel borane stabilizers may be usefully employed in emulsions comprising various silver salts such as silver bromide, silver iodide, silver chloride or mixed silver halides such as silver chlorobromide, silver iodobromide and silver iodochlorobromide.

The silver halide emulsions can be made with any of the macromolecular water permeable colloids known to be suitable for this purpose. Suitable materials include gelatin, polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, ethers and acetals, hydrolyzed interpolymers of vinyl acetate and unsaturated addition polymerizable compounds such as maleic anhydride, acrylic and methacrylic acid esters, poly-N-vinyllactams, polysaccharides, e.g., dextran, dextrin, etc., the hydrophilic copolymers disclosed in Shacklett, U.S. Pat. 2,83 3,- 650 hydrophilic cellulose ethers and esters and acrylamide polymers. Mixtures of these binders can also be used as Well as water permeable binding agents containing dispersed polymerized vinyl compounds such as those disclosed in Nottorf, U.S. Pat. 3, 142,568 issued July 28, 1964.

The emulsions utilizing the antifoggants of this invention can be coated on any suitable support, e.g., cellulose esters, cellulose mixed esters, superpolymers, e.g., polyvinyl chloride (co) vinyl acetate, polyesters, e.g., polyethylene terephthalate, polyethylene terephthalate/isophthalate, polycarbonates, polyesters formed by condensing terephthalic acid and its derivatives, e.g., dimethyl terephthalate with propylene glycol, diethylene glycol, tetramethylene glycol, cyclohexane-1,4-dimethanol (hexahydro-p-xylene dialcohol); paper, metal, glass, etc.

The invention will now be illustrated in and by the following examples but they are not intended to limit it in any way except as set forth in the claims.

EXAMPLE I A gelatino-silver halide emulsion containing 98.8 mole percent silver bromide and 1.2 mole percent silver iodide suitable for an X-ray film was prepared under proper safelight conditions. The emulsion was precipitated and ripened and was then washed and redispersed in the manner described in Moede, U.S. Pat. 2,772,165 issued Nov. 27, 1956. The pH of the emulsion was adjusted to between 6.3 and 6.4. The emulsion was then divided into portions as indicated by the number of samples shown in Table I. One portion was used as a control and to the other portions there was added 5 10 moles per 1.5 moles of silver nitrate of the borane compounds indicated in the table. Conventional gold and sulfur sensitizers were added and the emulsions were digested for 25 minutes at 120 F. Various addenda, e.g., preservatives, coating aids, etc. were added and the emulsions were coated on a polyethylene terephthalate photographic quality film base. The emulsions were overcoated with a conventional gelatin layer as is well known in the art of photographic manufacture.

Samples of the coated layers wer exposed for 5 seconds in an intensity scale sensitometer using a /2 step wedge, #2 lamp, Wratten #39 filter and a 1.8 neutral density filter. The samples were developed for 40 seconds at 88 F. in a conventional X-ray developer containing a small amount of 1-phenyl-3-pyrazolidone and hydroquinone.

The developed layers were fixed, washed and dried and the densities read on a transmission scale densitometer. D equals the highest density reading, fog equals processed density where not exposed. A second set of 4 samples was aged 7 days in an oven at 120 F. at 62% relative humidity and tested. These tests are designated 7 OT in the table. Sensitometric results are shown below.

TABLE 1 Coating Compound (5X107 moles/1.5 No. moles AgNO est Dam Fog 2 1 Noneoontwl "08 8 .133: 1:32 .38 .17 2 H2B12Cl12-XH2O(X 7 1 J7 1.41 .15 a 4)2 12 112 "fig? 1,28 .72 4 Hsh h uEL 3? J2 .19 a S2 12H1o( 0 )2 453% 1 37 .19 5s .13 6 CS2B12 r1o( a)2 1 88 .20 7 S2 12 1'11( s) .17 8 Natniznuooonn J4 .19 9

"fiat-.1; it? 4 .27 1o HBBHHMNHQ)? 12 EXAMPLE II A silver iodobromide developing out emulsion suitable for seismographic work was prepared under proper safelight conditions by adding an aqueous solution containing 1.5 moles of silver nitrate to an aqueous gelatin solution containing 1.55 moles of ammonium bromide and 0.015 mole of potassium iodide. The gelatin solution also contained 0.131 mole of strontium chloride. After precipitation, the emulsion was ripened by heating at 120 F. for 40 minutes. The emulsion was then cooled, washed and redispersed in the manner described in Moede, U.S. Pat. 2,772,165 issued Nov. 27, 1956.

The redispersed emulsion was divided into portions as indicated in the following table. One sample was used as a control. To the other portions, there were added the quantities per 1.5 moles of silver nitrate indicated in Table II of the borane compound,

The emulsions were digested at 120 F. for 30 minutes and cooled to F. The emulsions were optically sensitized with the dye, 5-(3-methyl-Z-thiazolinylidene-isopropylidene) -3-ethylrhodanine.

The usual coating addenda, e.g., antifoggant, coating aid, hardener, etc. were added and the emulsions were coatceld on a photographic quality paper support and drie The coated emulsions were sensitometrically tested according to the following procedure.

Strips were exposed for V of a second in an intensity scale sensitometer to a /2 neutral density step wedge using as a light source, a General Electric No. DMX sensitometer lamp operating at 82 volts and 4 amperes to give a color temperature of 2877 K. This provided 19.2 meter-candle-seconds at the focal plane. The material was exposed through a Wratten K2 filter. The exposed strips were developed for 45 seconds at 68 F. in a conventional metol hydroquinone developer. The developed strips were rinsed in a short stop bath, fixed and dried in a conventional manner and the densities read on a densitometer. In the following table, D equals the highest density reading, speed #1 is equal to /E at density of 0.10 and speed #2 is equal to 100/ E at density of 0.80. Total scale equals the number of steps between density 0.01 and D 0.03 and is a measure of contrast. Fog is indicated as 1 which is the density obtained after 45 seconds in the above developer without any exposure and as 3 which is the density obtained after 2 minutes and 15 seconds in the developer without any exposure. The samples were exposed fresh and after 7 days in an oven at F. and 62% relative humidity. Sensitometric results are shown in the table.

TABLE II C t Mole-550i H ni oi gmio a mg per mo es g a Total No. (X27) Test age Speed 1 Speed 2 scale Dmax- Fog 1X/3X 1 N one-Control ..{Fresh.-.. 946 279 8.0 1. 06 18/. 22 7 OT 856 109 13.5 91 28/. 31 2 X10- .A{Fresh. 656 279 7.0 1. 25 O2 7 OT 046 299 9. 0 l. 05 05/. 07 3 2.5)(10 A{Fresh 056 269 7.4 1.27 .01/.02 7 OT 916 279 11. 5 1.14 05/. 05 4 1 X10 ..{Fresh 636 270 9. 0 1. 26 01/. 02 7 OT 946 279 14. 0 1. 14 03/. 04

EXAMPLE III temperature of 3010 K. The material was exposed A gelatino-silver chlorobromide emulsion suitable for a variable contrast photographic element was prepared under proper safelight conditions wherein the silver halide contained 75% silver bromide. After precipitation of the silver halides the emulsion was ripened for 26 minutes at 110 F. and then chilled to set, noodled, and washed in a conventional manner to remove unwanted salts resulting from the silver halide formation.

The emulsion was then remelted and there was added to the molten emulsion a conventional sulfur sensitizer. The emulsion was digested for 60 minutes at 119 F. Ten minutes before the end of digestion there was added per 1.5 moles of silver nitrate, .034 gram of the optical sensitizing dye, 5-(3-ethyl 2 thiazolinylideneethylidene)-3- ethyl-2-thio-2,4(3,5)-oxazoledione. As the emulsion was cooling after digestion, it was divided into portions as indicated in Table III and to each portion there was added per 1.5 moles of silver nitrate, 0.01665 gram of 4-hydroxy- 6rnethyl-3,321,7-tetrazaindene, 0.52 gram of formaldehyde and quantities of borane compounds as shown in Table III. The emulsions were coated on photographic quality paper supports.

Samples of the various coatings were tested by immers ing one set in a conventional metol-hydroquinone developer for 1 /2 minutes with no exposure. This is designated as 1X in the table. Another set designated as 3X was developed for 4 /2 minutes without exposure. Samples were developed as above and after 7 days (designated as 7 OT) aging in an oven at 120 F. and 62% relative humidity which represents about 10 months shelf aging. The results are shown as follows:

TABLE III Fog 1 l3 Coat Moles of borane compound per No. 1.5 moles of AgNO; Fresh 7 0T 1. None-Control 015/. 036 .02/. O3 2 1111 1X10 T110185 [(CHa) 4Nl2B12I12. 02/. 04 0l./. 02 3. 5X10 moles [(CHa)4Nl2Bi2liz 01/. 07 02/. 03 2.5)(10 1110168 [(CHs) 4N12Br2l12 02/. 03 01/. 03 1X10 moles (NAQzBmBnz 03/. 03 01/. 02 5X10 moles (NI-102 121 112 01/. 03 02/. 02 1X10 1110183 HzBmChaXEIzO (X 03/. 05 01/. 02 2.5X10' moles H2B12C112.X1I20 (X 02/. 02/. 04 1X10- moles NazB12I1o(COOH)2 .01/. 03 005/. O2 5X10 moles NazBrzIMCOOH): 02/. 04 01/. 02 1 10- moles CSzBrzBrMNa)- 02/. 03 (11/. 02 5x10- moles CszBlzBriflNi)- 01/. 08 02/. 02 2.5)(10 moles CS2B 12 l11(Na). 02/. 02 01/. 01 1X10' moles CS2B1zBr1 (N3)2 01/. 03 02/. 02 5X10 moles CS2B 2B110(N:1)2 00/. 01 02/. 02 10- 2.5)(10' T110105 CS2B12B110(N3)2 .1 01/. 02 01/. 02

EXAMPLE IV An emulsion was prepared as described in Example III and divided into 4 portions after washing and remelting. Various quantities per 1.5 moles of silver nitrate of the borane compound, HzB gcl z as indicated in Table IV were added during the remelting operation. In addition to the fog tests as described in Example III, the samples of the material were exposed for 4 seconds in a conventional intensity scale sensitometer using as a light source, a sensitometer lamp, No. CPB sold by the Eastman Kodak Company which provides 39.5 candle power burning at 10 amperes and 4.6 volts which provides 117.5 metercandle-seconds at the focal plane. The sensitometer was equipped with a Wratten No. 82C filter to give a color through a /2 neutral density step wedge and through a Du Pont Filter No. 2 of a series of from No. 0 to 4 for variable contrast exposures, filter No. 0 giving the lowest contrast and No. 4 giving the highest contrast. The sensitometric and fog results are shown in the following table.

Example IV was repeated but only fog tests as described in Example IV were conducted and 14 day oven tests in addition to fresh and 7 day oven tests were also conducted with the following results.

TABLE V i N0. Antitogger Fresh 7 0'1 14 OT 1 None-Control .04/.14 17/. 43 39/. 2 1X10' moles H2B12H10(NH2)2/ .01/. 03 .04/.14 16/. 36

1.5 moles AgNOz. 3 5X10 moles CSZBI2BI'11(N3)/ .03/. 06 05/. 14 16/. 39

1.5 moles AgNOa. 4 X 0" 0 e s)4N]2 12I12/ 01/. 02 .08/. 22 .24/. 59

1.5 moles AgNO It will be clear to those skilled in the art that the practice of the invention lends itself readily to a wide variety of applications in the field of photographic silver halide emulsion manufacture. Therefore, it is not intended that the invention be limited except as set forth in the claims.

I claim:

1. A photographic silver halide emulsion prepared by adding a borane compound to said emulsion after the silver halide is precipitated and washed, said borane compound having the general formula a( 12 (12b) c where:

M is a cation;

X is an electrophilic moiety having a total valence of b; a is an integer from 1 to 2;

b is an integer from 1 to 12; and

c is an integer from 1 to 2.

2. A silver halide emulsion prepared as in claim 1 wherein said borane compound is added in amount of 10- to 10* mole per mole of silver halide in the emulsion.

3. A silver halide emulsion prepared as in claim 1 wherein said borane compound is H B Cl -YH O, where Yis about 7.

4. A silver halide emulsion prepared as in claim 1 wherein said borane compound is (NH B Br 5. A silver halide emulsion prepared as in claim 1 wherein said borane compound is [(CH N] B I 6. A silver halide emulsion prepared as in claim 1 wherein said borane compound is Cs B1 10(N 7. A silver halide emulsion prepared as in claim 1 wherein said borane compound is Cs B ;Br (N 8. A silver halide emulsion prepared as in claim 1 wherein said borane compound is Na B I10(COOH) 9. A silver halide emulsion prepared as in claim 1 5 wherein said borane compound is CS2B12H11(COOH) 10. A silver halide emulsion prepared as in claim 1 wherein said borane compound is Cs B H (COOH) 11. A silver halide emulsion prepared as in claim 1 wherein said borane compound is H B H (COOH) 12. A silver halide emulsion prepared as in claim 1 wherein said borane compound is H B H (NH borane compound to said emulsion after the silver halide is precipitated and washed, said borane compound having the general formula as set forth in claim 1.

References Cited UNITED STATES PATENTS 3,637,392 1/1972 Bigelow 96-109 3,563,746 2/1971 Ernst et a1. 96-109 3,451,819 6/1969 Haugh 96l09 NORMAN G. TORCH'IN, Primary Examiner W. H. LOUI'E, JR., Assistant Examiner US. Cl. X.R.

13. A silver halide emulsion prepared as in claim 1 15 96 11O wherein said borane compound is Cs B Br (N 14. An improvement in the process of making photographic silver halide emulsions comprising adding a 

